"The Aquarium Murder" by Stan Smith

Detective Rose Lopez of the Everett City Police had been to the city aquarium once before, years ago. The place seemed very different now at eleven-thirty at night, as a police team fished a man's body out of the tank that rose through the center of all three floors of the building. A circular ramp enabled visitors to view the tank's inhabitants.

A long-handled net was also removed from the tank. The man was laid on the third floor carpet by the side of the tank, away from a large blood spot. A cursory examination revealed his fatal knife wound.

"It's Jack, Jack Boxer," confirmed Helen Fogg, who sat nearby. She wore a khaki custodial uniform like the victim's. "We had been cleaning on the second floor, as we usually do between ten and eleven. He went up the back stairs at ten-thirty to get a head start on Three. Then I heard him scream up there. I ran up the ramp, but found nothing but the blood spot. Henry the guard came up the ramp behind me. Then he went back down to let in the police."

"Why did Boxer go to the third floor early?" asked Lopez.

"Jack wanted to leave early and start on his vacation trip to Vegas. We cover for each other."

"What were you doing when this happened?"

"I was wiping down some of the displays on Two, and getting ready to shampoo a section of carpeting."

Lopez walked down the ramp to the second floor and paused to check the janitor trolley still there. The empty trash barrel was surrounded by several cleansers and rags, and the carpet shampooer stood alongside.

At the first floor desk, Lopez found Henry Shanosky, the guard, waiting behind the front desk.

"I came on duty at seven," he told Lopez. "Made my round when I arrived and again at eight-thirty and ten. Mr. Denny, the accountant, was working in his back office. Jack and Helen arrived at eight. When I heard the scream from upstairs, I pushed the button that locks the outside doors both ways, hit the silent police alarm, and ran up. Helen was already there and pointed out the blood spot. It was the cops who found Jack in the tank."

"What were you doing when not on rounds?" Lopez asked, observing the splint on the guard's left thumb.

"I was here at the desk, doing logic puzzles. It's my hobby."

Lopez then visited the small office of Charles Denny, the aquarium accountant. One of the uniformed officers had stayed with him. When Lopez introduced herself, Denny got up and shut off an old, noisy dehumidifier. The silence was so sudden that the drop of condensation spattering the bottom of the catch-pan startled her.

"I don't mean to seem callous, detective," Denny said tartly, "but I have to keep working tonight. Our fiscal year ended a couple of weeks ago, on June 30, and our auditors need preliminary numbers tomorrow. I'm sorry Jack is dead. As I told the officer, I know nothing about it."

"You heard no scream?"asked Lopez.

"No chance." Denny jerked a thumb at the dehumidifier. "Had this on all evening, and couldn't hear anything else. It helps me concentrate, actually. Except for running out for a sub and soda at six, I haven't left this office. I was some surprised to see your officer walk in, I can tell you."

"Your window looks onto the parking lot." Lopez tested it; it opened laterally only about a foot. "Have you seen anyone out there in the last two hours?"

"I had my back to it. Never looked at it."

The next morning Lopez sat wearily in the office of her boss, Lieutenant Gary McDonald, as he reviewed preliminary reports on the case.

"There were three sharks in the tank," he remarked. "Just as well they weren't hungry. The aquarium director speculates that the killer might have been trying to retrieve one of the rare scarlafish, which are worth several thousand on the exotic fish market. The net was taken from the lab in back of the second floor, and a two-gallon plastic storage case was found there, tossed in a corner and still wet."

"That could explain a few things," said Lopez. " The killer could have been trying to net the scarlafish and been surprised by the victim. Killer stabs victim and slips him into the drink, figuring that the sharks might finish him and make it look like he fell in accidentally while trying to steal the fish himself."

"Maybe. But then why return the storage case to the lab?"

"A panicky mistake." Lopez leaned forward. "Boss, I think I know who did this."

So...whodunit. Was it Helen Fogg, Henry Shanosky, or Charles Denny

Please after it is solved post another. I don't want this to die

Hmm... sounds like Charles Denny, really. The dehumidifier seems to tell me she was trying to dry something up. But I haven't been reading this puzzle too well, so I could be wrong.

Here's the key to the whole thing. ;)

The giveaway was that too much attention was paid to this paragraph, the author really went out of his way to point out 'hey, there's a dehumidifier!!!'

If a dehumidifier runs all night, it should be full of water, you wouldn't hear drops hitting the catch-pan, you'd hear it 'drip-drop' or hear nothing at all.