MEXICO CITY (AP) — A grisly pre-Christmas killing of two young men and their uncle at an early 1900s house in Mexico City cast attention on the dark side of the capital’s booming real estate market, fed by a lack of legal documents and gangs that illegally seize properties.

Actor Andrés Tirado, his musician brother Jorge Tirado and an uncle whose name was not released were found dead Sunday, all with their throats slashed. Prosecutors said the apparent motive was an ownership dispute over the property.

In another case, a young woman on Tuesday posted a desperate video on social media from a rooftop on the city’s south side in which she can be heard screaming: “Police! Help! They have kidnapped me!”

Police said the woman told them relatives had erected a metal door to prevent her from leaving her home, trapping her inside with four children. Police said a dispute over property ownership was behind the alleged abduction and that an investigation was underway into the illegal takeover of the property.

Authorities have known for years there are armed, violent gangs that specialize in taking over houses. The trend is enabled by the fact that many properties — perhaps as many as one-fifth of homes — have no legal papers or have titles listed in the names of dead people who left no will.