Walk with him down just about any thoroughfare in the center of town, and he'll point out where someone drew their last breath. "Prague's not New York yet," says the 42-year-old chief of criminal investigations for the Prague Police, but it's coming along, with 45 to 50 murders a year.

And, adds Mareš, "In Prague, you always get the interesting ones."

The trim and chiseled top detective, who favors Nike tennis shoes, black jeans and polo shirts and does not allow his face in the papers, knows of what he speaks.

Having studied mechanical engineering in university, Mareš made the switch to law enforcement after the Velvet Revolution in 1990. It was a tumultuous time, he recalls, with the entire structure and role of the police in rapid transition; the guardians of the state were learning to be protectors of the public.

It's a transition still in progress, say some, but Mareš proved to be just the sort of fresh blood the lumbering Prague force needed. In three short years, he made it to homicide, the division every ambitious cop dreams of.

By 2000, Mareš was chief of the 40-officer homicide section, made up of colleagues whose average age is 50, some of whom have been there 20 years. Earlier this year, he rose to chief of criminal investigations, where he now supervises 600 officers.

It's not something you'd guess from a look around his cramped Prague 2 office: the standard-issue municipal rabbit hole in a grim concrete tower, complete with glass-fronted cabinets along the walls, an institutional-style desk and a scrawny plant or two fighting for life.

A few décor choices do make it unique, however, such as the Chinese ornamental machete he keeps as a prize from a gang fight in which a man was badly hacked. ("When Czechs argue, they might slap each other," Mareš says, "but these guys from the former Eastern bloc get out the knives.")

"You'd never have guessed he was a killer," he says quietly. "The media didn't show any interest in the case. I feel that if I hadn't gone there at the time to investigate, the murder would have never been punished. The local department would file it as an accident, and that's where it would end."

As in most cities, 99 percent of homicides are clear-cut cases of violent death, Mareš explains. This one was classed an accidental fall until he began reviewing the details and noticed an odd problem. How does an elderly woman, falling by accident while hanging out the laundry to dry, land 7 meters (23 feet) from her wall?

To find out, Mareš visited the scene of the crime several times, each time asking a bit more about who was where when it happened, finally bringing in his video camera and a firefighter to simulate the fall while suspended by ropes. (For more details, see "In His Words.")

The killer's face began to tell as much as the climber's movements, recalls Mareš, chuckling as the tape rolls.

It turns out a working knowledge of biomechanics can be an asset in police business.

"Every murder case is different, and that's what's beautiful about it. You can never tell in advance whether it will be simple or complicated."

Take the Orlík reservoir murders, for example, which inspired the less-than-inspiring Czech film Velvet Murderers. In that case, in which an unrelated investigation led to the discovery that several bodies had been dumped at Orlík in oil drums in 1995, Mareš learned a lesson he'll never forget about how badly the media can screw up a case.

"We worked undercover, posing as environmentalists," he said about police efforts to check out the reservoir in south Bohemia. "Nobody knew we were police officers. However, TV Nova showed up at the scene on Saturday with no idea what we were looking for, but they did know we were the police — I don't know who told them."

Shaking his head, he recalls, "It was on television. We had witnesses with us who were instantly endangered by this, as the culprits were still running free. I didn't sleep for two days, stayed in my office, filing house-search and arrest warrants." All this because the media smelled a hot story.

"On the other hand," he says, "we do need the media when publishing information or photos and asking for witnesses to offer their testimony."

Earlier this year, Mareš says media coverage indeed paid off with the arrest of "a Slovak peroxide blonde," who, with her lover, was a traveling performer who had plotted to separate a retired Italian cop living in Prague from his life savings.

"We worked really long on that case. We knew who the culprit was, we had her picture, her image appeared on television and in press, and then the circus owner called to say that they were with his circus."

The Prague murder clearance rates are something to be proud of, Mareš says, particularly in that killings have become more violent and more are tied to gangs these days than ever before. In the past year, four murders resulted from robberies; none did in 2004.

All in all, it's a job that demands an unconventional mind and the energy of a man in his prime. The city can breathe a sigh of relief in that respect, at least.

For the foreseeable future, anyone thinking about taking an enemy out of the picture will find himself going up against a calm, cool cop who doesn't flinch.