EDINBURG, TEX. ? Six men were tied up and shot to death early Sunday in a Lower Rio Grande Valley rural subdivision outside Edinburg in what police described as a home invasion gone wrong.

Police said they were investigating several possible motives for the city’s worst homicide case in recent memory. No arrests had been made by early Sunday.

A witness, the mother of two of the shooting victims who was tied up with electrical cords during the slayings, told Edinburg police the killing began around 1 a.m. Sunday when four or five men in ski masks, and one wearing a jacket that read “police” burst into the woman’s white frame house.

The witness said she and one of her sons were tied up as the assailants searched her home for guns and drugs, said Edinburg Police Sgt. Rey Ramirez.

The search continued to a shed-like home also on the property where the woman’s other son and four acquaintances were staying, according to the witness.

The assailants tied up the five men in the shed and shot them repeatedly in the head and chest, police said.

They then returned to the main house, forced the woman to turn her head to the wall and shot her son.

The woman told police the killings took place over 15 to 20 minutes. She managed to untie herself and run to a neighbor’s home to call police about 10 minutes after the assailants left.

Neighbors reported hearing shots fired but did not see anything, Ramirez said.

“It’s a shock,” neighbor Carlos Lopez, 59, told The Associated Press. “All I heard was shots … about six or seven or eight.”

He said he didn’t hear any cars spinning out that he would associate with the assailants. Lopez lives about 20 yards away from the investigation site.

“It’s scary. You never know. They might sometimes get confused and get the wrong house. It’s hard, especially for the mother,” he said.

The names of the victims and survivor were not released Sunday night. Ramirez said police knew two of the men from previous investigations, but he wouldn’t elaborate.

During the past year, there have been several incidents in Edinburg in which people pretending to be police have invaded the homes of suspected drug dealers and stolen money, drugs and weapons, Ramirez said.

“This is the first time that anyone was killed,” he said.

The killings mark the first homicides of 2003 in Edinburg. “We only had five homicides all of last year,” Ramirez said. “We were just saying that we hoped this year would be less.”

Edinburg is about 220 miles south of San Antonio near the Texas-Mexico border.