Murder Mystery... Who-dun-it?

I've always loved brain teasers and murder mystery games. I'm a huge fan of the tv show Monk. I stumbled across some short murder mysteries. Today's blog contains one of the mysteries. See if you can figure out who the murderer is...

"The Creekside Killing" by Guy Belleranti

Sheriff Dave Dark stared down at the body of Frank Cullen, being careful of where he stepped. He didn't want to mess up the crime scene. He also didn't want to get any more mud from the creek bank on his brand new boots.

That Cullen had been shot in the head was obvious. Who had done it was not. The most likely suspects were Cullen's three fishing buddies-- Greg Walsh, Carlos Melendez, and Sam Pelgoni. The men had rented the little cabin just up the hill from the creek for the weekend.

Dark climbed back to the cabin where Deputy Spencer was holding the three men for questioning. He took a few steps inside and stopped, looking sheepishly at the muddy tracks he'd left on the clean wood floor. He also noticed he was alone in the cabin. "Spencer?" he shouted.

"Sorry, sir," his deputy said. He was out of breath from running up to the doorway. "I thought we'd all wait out here for you."

Dark followed Spencer to a picnic table sitting beneath a small stand of aspen. He stood at one end and studied the three men-- Walsh and Pelgoni on one bench, Melendez on the other. "All right. Let's hear about everyone's whereabouts at the time of the murder. You first, Mr. Walsh."

Greg Walsh fingered his red goatee. "I don't know where I was when Frank was shot."

"I thought you said you heard the shot," Spencer said from behind Dark's shoulder.

"I heard a shot. Don't know if it was the shot. It's hunting season, so you do hear the occasional shot."

Dark scowled. "Where were you when you heard this one?"

"Upstream." Walsh pointed. "Around the bend. I thought a hunter may have gotten too close to our camp. I didn't see nothing till I got closer. When I saw Frank... I started up to the cabin, spotted Carlos getting out of his truck, and yelled for him to call 911. Then I ran back-- to, uh, to stay by Frank."

The sheriff cocked an eye at Carlos Melendez. "Where had you been?"

"In town -- getting grub and beer. I ran into the cabin to make the call and found Sam already taking care of it."

"I guess I was the first one on the scene," Pelgoni explained. "I was fishing down the other way when I heard what sounded like a gunshot. I turned and saw Frank falling. I hurried over to his side, saw the wound and--" He ran a hand through his gray-streaked hair. "I figured I'd better call for help fast."

"Any of you got an idea who'd want to kill Cullen?"

"Nope," Pelgoni said. "Can't understand it. He was a great guy."

"Sure was," Walsh agreed. "It's gotta be some sort of freak accident. Someone was out hunting and shot Frank by mistake."

"Hmm." Dark chewed at the corner of his mustache. "How about you, Mr. Melendez? What do you think?"

Melendez flushed, glanced at the other two fishermen, then looked away. "I think it's tied in with that bank robbery in Pinedale the other day."

"Bank robbery--" Pelgoni began.

Dark held up a hand. "Quiet!" He swung back on dark-haired man. "Go on."

"Well, early this morning-- around sunrise, I guess-- I got up to use the can and saw Frank pacing around outside like a crazy man. I went out and asked him what was wrong and he-- he started blubbering like a baby. Said he had done a terrible thing. That he and another guy had knocked off the bank yesterday afternoon before we all met here, and that a customer in the bank had got hurt."

"Did he say who his partner was?" Deputy Spencer asked.

"No. But I think I had him convinced he should go to the cops."

Sheriff Dark stared at Melendez long and hard, then at the other two men. "You fellows all arrived separately yesterday?"

"Yeah," Pelgoni said. "And I had nothing to do with any bank stickup."

"Me either," Walsh said. He glared at Melendez. "You sure you didn't dream this up in the morning sun?"

Melendez stuck out his jaw. "I'm telling the truth. And Frank's getting shot proves it. Someone didn't want him to talk."

Everyone looked at Sheriff Dark who shrugged. "I don't know what the motive was, Mr. Melendez. But I know the killer. There's one clue that gives him away."

Who killed Frank? What is the clue?
Greg Walsh
Carlos Melendez
Sam Pelgoni

See comments for the answer. No cheating!