Photo: Garden Grove Police Department

Maria Teresa Lopez, 65, and Jesus Ruben Lopez Guillen, 70, were reported missing by their daughter in Garden Grove, Calif.

A Southern California couple who wentmissing in Mexicoafter going to collect rent money from their tenants have been found dead and presumably murdered.

The bodies of Jesus Ruben Lopez Guillen, 70, and wife Maria Teresa Lopez, 65, were discovered buried underneath the floor of a home in Tijuana on Thursday, theSan Diego Union-Tribunereports.

The couple’s son-in-law, who authorities identified as “Santiago N,” was arrested in connection with their deaths the same day, according to the Tribune. Police suspect their deaths may have been over a monetary dispute,KTLAreports.

In another twist, on Saturday, Tijuana police found two additional bodies of a man and a woman buried in the same home, according toKABC. Those victims have yet to be identified.

On Sunday, a judge ordered that Santiago remain in custody on a “forced disappearance” felony charge, theTribunereports. He has not been charged with any crimes at this point, theTribunereports.

“They own some properties in Tijuana and they go down to collect rent and take it to the bank and there is a place where they would exchange it,” Garden Grove Police Department Lt. Carl Whitney told PEOPLE. “They were going to have the money exchanged and do a quick turnaround trip and be right back.”

The couple’s daughter told police that she tracked her parents to one of their properties using an online service, but when a relative went to check on them, they weren’t there. The phone later died.

Want to keep up with the latest crime coverage? Sign up forPEOPLE’s free True Crime newsletterfor breaking crime news, ongoing trial coverage and details of intriguing unsolved cases.

Tijuana police discovered the pair’s green 2005 Toyota Tundra near the rental property, Whitney said.

According to theTribune,Santiago told authorities that he picked up the couple at the Tijuana border crossing, took them to their rental properties and later brought them to a bank to exchange the rent money into U.S. currency. He then alleged he brought the couple back to the border.

Prosecutors said they discovered “several contradictions” in his statements, theTribunereports.

source: people.com