TIJUANA, MEXICO (CBSLA) — A fifth body has been found at a Tijuana home where the bodies of a Garden Grove couple were found.

Jesus Guillen, 70, and his wife, 65-year-old Maria Lopez, drove into Tijuana on Jan. 10 to collect rent from their tenants, and were never heard from since. Their bodies were found last Friday, buried in mud at one of their properties.

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A second set of bodies – also male and female – were discovered late Saturday in a state of advanced decomposition. The discovery of a fifth body was announced by Mexican authorities Monday.

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Their son-in-law, identified by Mexican authorities only as Santiago N., has been arrested in their murder. The 36-year-old man had previously been deported from the United States in 2012.

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Mexican authorities say he had been collecting rent for apartments they owned in the city on their behalf, and they suspect he killed them in a dispute over money. Investigators also said they believe the suspect wanted to stage a kidnapping in order to collect ransom.