So the reason why Dumbledore and Harry still risked so much for this Horcrux though they had the locket is because they had no idea which Horcrux it was until the potion is gone and they see it is the locket, a fake. I take this from the movie. I'm sorry if it was confusing.

Harry was racing after Snape, having wasted too much time already. He could see the cloaks of the Death Eaters billowing behind them as they ran. He petrified one, stunned another, and immobilized a third. He was running, panting, ignoring the battle raging around him. He tripped over a body, glanced back and saw the red hair of Ronald Weasley. He shoved the thought out of his mind, stood, and started off again. His throat burned. White blotches kept edging in around his vision. Hot lava was swishing around in his stomach. He kept running. He didn't even feel the cold air slam into his face when he bolted from the castle. Before he knew it he was approaching Hagrid's. It registered a whole minute later that the house was on fire and panic welled up in him.

"No!" He screamed. "Leave him alone! You won't take him too!"

He tried to stun Snape, but missed and he saw Draco dash into the trees. The Potions Master spun around, raising his wand.

Despite all the emotions smashing most of Harry's logic, he managed to still not speak as he cast. Snape parried, knocking Harry off his feet. There was another bang inside Hagrid's hut. Hagrid was yelling, but nothing he said made sense. Harry was on his feet again. He tried to torture Snape again. This time it worked, but only momentarily. It was no long torture like what Harry had seen in the past. Just a moment, just enough to throw Snape down to the ground. He stood quickly, looking livid.

"You haven't got the nerve nor the ability to cast a true Cruciatus!" Snape bellowed at him, aiming his wand at Harry.

Harry tried another spell, but Snape deflected it lazily.

"Fight back!" Harry shrieked. "Fight back, you cowardly..."

"Coward, did you call me, Potter?" Snape shouted. "Your father would never attack me unless it was four on one, what would you call him, I wonder?"

He threw out a stunner, but Snape blocked it.

"Blocked again and again and again until you learn to close your mind, Potter!" Snape roared before speaking to another Death Eater. "Now come! It is time to be gone, before the Ministry turns up..."

Impedi...

Pain erupted through his body and he fell, screaming, and he was sure he would die for how much it hurt.

"NO!" It was Theodore's voice (though he swore he heard Snape as well) and the pain stopped when he spoke. "Have you forgotten your orders? Belongs to the Dark Lord...leave him! Go! Go!"

Harry wasn't done though. He yanked himself to his feet, aimed his wand at Snape, cleared his thoughts, and cast.

Someone had yanked him down and the spell soared past Snape's head, grazing the man's cheek and hitting a tree.

"You dare!" Snape roared angrily as Harry tried to wrestle away from Theodore. "My own spell! You'd turn my inventions on me, like your filthy father, would you?"

Harry's elbow landed hard against Theodore's face. He heard some crack, felt the blood as it dribbled down onto him. Shoving the boy off, Harry dove for his wand.

"No!" Snape hexed it and the wand flew feet away.

"Kill me then!" Harry thundered. Theodore was on his feet, wand out and aimed at Harry. "Kill me like you killed him, you coward..."

"DON'T..." Snape suddenly looked insane, eyes wide and skin white as if he was in pain. "CALL ME A COWARD!"

He slashed at the air with his wand, but Theodore had jumped in front casting a shield charm. Several moments passed and by the time Theodore lowered the charm, Snape had gone. Harry tackled him the moment he realized Theo had permitted his enemy to escape.

"You bastard!" Harry pinned Theodore down and began to punch him, fury blinding him. "You bastard! You knew! You helped! You were working for them all along!"

A spell threw him back and he picked himself up off the ground only to find Theodore, face bloody and bruised, pointing his wand at Harry.

"I did what I had to." Theodore snarled, blood and spit flying from his split lip. "And it's not as if you didn't know! You knew who's side I was on! You saw!"

"I trusted you!" Harry shouted back. "Last year you refused to help him!"

"Last year was different." Theo replied. "Last year I wasn't looking the Dark Lord in the face and getting told that if I didn't do as he said he'd kill me! And I told him anyways! I refused to do as he asked because I knew you'd never forgive me!"

"And I'm supposed to be okay with the fact that you helped?"

"I HARDLY HELPED!" Theo howled. "I told Draco how he should have done it! I told him he should have used the curse, but he refused! He couldn't kill face to face! I knew it! I gave him ideas on how to sneak things through, but I knew they'd never make it! I knew in the end that it would be one of the Death Eaters! In all honesty, I didn't suspect Snape. One of the others, but not him! But even he knew it would be done! There was no getting around it! Dumbledore was going to die one way or another!"

"NO!"

"Did you not see his hand?" Theo barked. "I know you did! You kept pointing it out and worrying about it! It was cursed! It was killing him! He was going to die anyways!"

"He didn't need to die like that!"

"And why not? You preferred for him to die slowly then? Painfully? Tortured? You're a worse friend to him than you always played off."

"Shut up! SHUT! UP!"

"HE WAS DYING! What Snape did tonight was more mercy than anything else! How do you know that Dumbledore didn't ask him to do it?"

"He was begging him! He begged him! He said 'you promised' and 'you gave me your word'!"

"And did he clarify what he was begging for? To be saved from the Death Eaters? Or to die?"

"SHUT UP!" Harry shrieked.

"Wha's goin' on?" Hagrid's booming voice lowered Theodore's wand and Harry dove for his, grabbed it, and aimed it at Theo.

"He's a..." Harry's words stuck in his throat as he stared at the wide blue eyes of Theo. He should say it. He should tell the whole world what Theodore was, but...his throat burned and his heart was pounding so hard he swore it was going to smash itself to oblivion against his chest. His wand lowered. "He's...we...Hagrid...are you all right?"

"'Course I am..." He glanced between them concerned. "Take more'n that ter finish me. Wha's goin on, Harry?"

"We should put out your house." Harry said, realizing abruptly he wasn't prepared to say what had happened. "The charm's 'Aguamenti'..."

"Knew it was summat like that."

Hagrid, Harry, and Theo each turned to put out the house.

"S'not too bad." Hagrid spoke hopefully. "Nothin' Dumbledore won' be able to put righ'..."

Harry's stomach hurt at the sound of the name.

"Hagrid..." Harry began, but Hagrid wasn't listening.

"I was bindin' up a couple o' bowtruckle legs when I heard 'em comin'." Hagrid was saying. "They'll've bin burnt ter twigs, poor little things..."

"Hagrid..."

"But what happened, Harry? I jus' saw them Death Eaters runnin' down from the castle, but what the ruddy hell was Snape doin' with 'em? Where's he gone...was he chasin' them?"

"He..." Harry cleared his throat. "Hagrid, he killed..."

"Killed?" Hagrid seemed bewildered. "Snape killed? What're yeh on abou', Harry?"

"Dumbledore. Snape killed...Dumbledore."

Hagrid was looking at him with blank features.

"Dumbledore wha', Harry?"

"Is dead." Theodore cut in and Harry felt relief flood him at not having to repeat himself again. "Snape killed him."

"Don' say that." Hagrid gave Theodore a glare. "Snape kill Dumbledore...don' be stupid, Theo. Wha's made yeh say tha'?"

"I saw it happen." Harry told him.

"Yeh couldn' have."

"I saw it, Hagrid."

Hagrid was shaking his head, disbelief on his face.

"What musta happened was, Dumbledore musta told Snape ter go with them Death Eaters." Hagrid told them. "I suppose he's gotta keep his cover. Look, let's get yeh back up ter school. Come on."

Theo opened his mouth to refute this claim, but Harry shook his head and he shut his mouth again. They walked up to the castle and through the gathering crowd to where Dumbledore lay. Harry didn't say anything and just collapsed beside him. Carefully, he straightened the half-moon spectacles on Dumbledore's face and wiped away the trickle of blood at the corner of his mouth. Then he just sat there, staring, unable to do anything and then, recalling that they had spent hours weakening Dumbledore to the point of helpless on a Horcrux that was fake, he found he could not contain his tears any longer and he finally started to cry.

Almost done.