Though the detective sees no obvious signs of trauma on the body of the woman in the tub, he starts to suspect foul play, not an accidental drowning.
That means the on-duty homicide detectives of Phoenix's C-32 squad, Jack Ballentine, Jason Schechterle and Tom D'Aguanno, will assume the investigation.
They get to the La Quinta at 2 p.m. Ballentine will be the lead detective, and D'Aguanno will take the scene. New to the homicide unit, Schechterle will do what Ballentine tells him to do.
The murder detectives take note of the amount of clutter in Room 121, including the 20-plus Bud Light empties.
"Gotta be a homicide," says Sergeant Patrick Kotecki, chuckling. He and his detectives know how often Bud Light seems to show up inside their crime scenes. One witty squad member has dubbed it the homicide squad's official beer.
But Ballentine doesn't know yet if he's going to be investigating a murder. "Sometimes it may look like homicide when it's not," he says. "But when we finally go in, I'll assume it's a crime scene until we find out otherwise, and that someone killed her."
To be on the safe side legally, Ballentine closes down the room until securing a search warrant from a judge. That will take a few hours.
While the other detectives wait for Tom D'Aguanno to return with the warrant, they interview motel employees and try to sort out who had been renting Room 121.
They learn that a man whose Mexican driver's license identified him as Felix Garnica had checked into the room with another Latino at 8:30 a.m. on April 17. The cost was $66.12, which Garnica paid in cash.
Garnica also rented Room 149 -- for a relative, he'd told the clerk in broken English. Garnica later paid for two more days in both rooms.
Just before 3 a.m. on April 20 (the day the woman's body was found), the motel clerk happened to see a man, not Garnica, leave Room 121 and head to the lobby.
That man's ID card listed him as Mexican citizen Silvano Ramirez. He rented Room 304 -- the "Presidential Suite" -- for $77.
The detectives go to see what rooms 149 and 304 look like. Both have been vacated, and housekeepers already have cleaned Room 149.
According to the staff, Room 304 seems not to have been used at all.
Knowing they'll be working late, the cops walk to grab a bite at a Denny's that shares a parking lot with the La Quinta. An officer stands guard at Room 121, which has been cordoned off with yellow crime-scene tape.
Just after the cops order at about 3:30 p.m., La Quinta's manager comes by to say a woman has just phoned after hearing on the radio about the unidentified female's death.
The caller is saying the dead girl may be her missing sister.
"This just got a lot easier for you, right?" the manager asks Jack Ballentine.
"Yeah, right," the detective responds drolly.
Canceling his food order, Ballentine walks back to the motel office to speak with the caller, who's been holding on. But a few minutes later, the detective hangs up the phone, shrugs and announces, "Not our gal. Doesn't fit at all. Too bad."
The detectives reenter Room 121 with the warrant at 4:30 p.m.
Besides the bloody pillow case on the nightstand, they see towels in the bathroom that also have bloodlike stains on them.
It will be a few hours yet before they examine their victim, if indeed she is a victim of a crime.
Detective D'Aguanno and an assistant document the evidence in the room, taking measurements and photographing everything before carefully placing it all into plastic and paper bags.
They find a receipt from a Wal-Mart dated just after midnight on April 20, within hours of the woman's death.
The investigators strike gold inside a small black backpack on a chair, in terms of identifying the person whose body lies in the bathtub a few feet away.
It contains an identification card from Mexico with a fingerprint and photo of a pretty girl laminated onto it, bus tickets from Oaxaca, personal photographs, and handwritten sheets of phone numbers and addresses.
The ID card is signed by Margarita Parada-Alavez from Oaxaca, with a date of birth listed as July 20, 1985.
Phony Mexican ID cards are as common as are taco stands on the U.S.-Mexico border. But it's a starting point, and the detectives start to suspect that the body in the tub may be Margarita's.