The gunman had not surrendered Sunday evening. Gunfire broke out again shortly before 8 p.m. and several officers wearing gas masks could be seen moving into the building where the gunman was holed up.
Officers were initially called to the apartment complex because of a report of a broken window in this town about 25 miles southwest of Dallas, Midlothian police said.
The officers determined the window had been broken by a gunshot and went to the apartment where they believed the shots had been fired. There, police said the gunman opened fire.
Trooper Rick Smith was shot as he responded to the report of three officers being wounded, said Lisa Block, a Texas Department of Public Safety spokeswoman.
Kim Gladney, 25, who lives in the complex, said she heard 10 shots ring out.
"After the first five, I knew something was wrong," she said as she stood just beyond the police barricades. "It just didn't sound good."
Midlothian police Sgt. Brian Woolery was in serious condition at Methodist Dallas Medical Center Hospital, spokeswoman Kathleen Beathard said. Officer Dustin Compton was in good condition and Smith was in fair condition. The fourth officer, Cody McKinney, was in fair condition.