NEW YORK — This January, a 21-year-old Canadian tourist named Elisa Lam disappeared while visiting Los Angeles. Lam was last seen at the Cecil Hotel in downtown Los Angeles, where she had been staying.

Tuesday, her body was found at the bottom of one of the hotel's rooftop water tanks, thus solving two separate mysteries at once: "What happened to Elisa Lam?" and "Why is the water pressure so bad at the Cecil Hotel?"

The hotel's guests were horrified at the news, with good reason — nothing spoils a vacation faster than learning you may have been brushing your teeth with corpse-water.

But anyone familiar with Los Angeles' history couldn't have been too surprised. Downtown L.A. has long been seedy, and somewhat dangerous; the Cecil Hotel, for its part, has a long and sordid criminal history.

The Cecil doesn't advertise its dark past; caveat emptor and all that. But, still, many guests might balk at staying in a hotel that was once a crime scene. It's best if you do your research before embarking on your travels, not after. Here are some ways to determine whether or not you might have booked a room in a murder hotel.

The hotel is also a residential hotel.

Half the time, people who live in hotels are either eccentric millionaires or adorable, adventure-prone children. The rest of the time, they are usually creepy drifters. Sometimes it's hard to tell which is which, so corpse-wary travelers should play it safe and avoid hotels that court the long-term trade. The Hotel Chelsea, where Sid Vicious allegedly killed Nancy Spungen in 1978, was also a long-term residential hotel. The Cecil is one, too; a Los Angeles Times article about the Lam case featured quotes from an 89-year-old man who has lived in the Cecil for 32 years. A hotel like this is probably not the sort of place you want to stay, unless you are a character in a Charles Bukowski novel — in which case, congratulations on magically coming to life!

Half the online reviews are left by people with names like "The Night Stalker."

A little Googling will reveal whether any serial murderers have ever used your chosen hotel as a kill site. Indeed, a quick search for "Cecil Hotel" and "serial killers" would've turned up a bunch of pertinent information. In 1985, Richard "The Night Stalker" Ramirez used the Cecil as a home base during his months-long murder spree in which he killed 14 people. (As far as I know, he did not actually kill any of his victims in the hotel.) An Austrian author and ex-convict named Jack Unterweger stayed at the Cecil in 1991 while in town researching a story on L.A.'s red-light district. Apparently Unterweger never learned that good journalists shouldn't make themselves part of the story; he murdered several prostitutes over the course of his stay.

The hotel seems to court the sex trade.

Last year, just like every single year before it, "prostitutes" took the top prize at the Groups of People Most Likely to Be Killed in Hotel Rooms Awards. This is why squeamish travelers should stay away from hotels that rent rooms by the hour, or boast that their staff is "discreet." A few years back, I used to stay overnight at a hooker hotel in the heart of the East Village. The hotel was really cheap, and thus I was willing to overlook the bulletproof glass at reception, and its pay-in-cash policy, and the giant mirrors next to the beds so that self-absorbed johns could watch themselves in flagrante. Turns out that some people also used the mirrors to tell whether the prostitutes they had just strangled were still breathing. I don't stay at that hotel anymore.

The room smells like corpses.

At some point in your life — probably while you were driving across Pennsylvania or something — you may have rented a room in a cheap motel, opened the door, sniffed the air, and yelled "Who died in here?" Often, the answer is "the previous occupant." Stories abound of corpses stashed under hotel beds, often for inexplicable lengths of time; in 2010 — and this is the most extreme case I could find — a Memphis woman named Sony Millbrook mouldered under the box springs of a bed at the Budget Lodge for six weeks before being found. If your room smells like death, don't just send down for some air freshener. Find a better place to stay.

The website is inept and hostile.

Most respectable hotels put a lot of time and effort into their websites, which is why you should be very suspicious of hotel websites that look like they were created with Microsoft FrontPage 97. Take New York's Hotel Carter, for example, a notoriously dirty Times Square hostelry known for its body count: a woman thrown out of a window, an infant beaten to death, a goth rocker stashed under a bed, a hotel clerk killed by another hotel clerk. Its website is inept, ungrammatical, and at times perplexingly belligerent. "We do not receive package/shipments for guests. We will refuse to receive package to those who order online and use our hotel address," the home page states, emphatically, in red italics. You know what else is red? Blood. A clear sign that this might be a murder hotel.

The closet is actually a chute leading down to a secret murder chamber.

Not to take anything away from turn-of-the-century serial killer H.H. Holmes — whose terrible true story was told in Erik Larson's "The Devil in the White City" — but come on, victims. Do a walk-through before you put a deposit down on a room. If you see any unexplained trap doors, leave.

Peters writes Slate's crime blog. @slatecrime.