AUSTIN,Texas - Police in Austin say "similarities" between three package explosions in Texas' capital city this month, two fatal, lead them to believe the incidents are related. The latest fatal incident, reported Monday morning, killed a 17-year-old boy and wounded a woman, Austin police chief Brian Manley said.

The boy died at the scene and the woman in her 40s was taken to the hospital with potentially life threatening injuries after the explosion at the East Austin home before 7 a.m. In an earlier incident March 2, Anthony Stephan House, 39, was killed when a package exploded at his northeast Austin home, CBS affiliate KEYE reports. 

Police also responded around 11:50 a.m. Monday to the report of an explosion in southeast Austin in which a woman was badly injured. Police received multiple calls about an explosion, Manley said at a press conference Monday afternoon. The victim in the incident came outside of her home to retrieve a package left on her front step, which exploded.

She is a 75-year-old woman and is listed in critical but stable condition, Manley said. Her injuries are considered life threatening.

"This is the third in what we believe to be related incidents," Manley said. 

Manley said a task force had been formed to investigate the incidents. He urged residents to be careful and not to open suspicious packages. If residents encounter any packages left at their homes they aren't expecting, he urged them to call 911.

"It's not time to panic, but it's time to be vigilant and it's time to pay attention, it's time to come together as a city and solve this,"  Manley said.

In the two previous fatal incidents, the packages were also left at the doorstep of the home apparently in the overnight hours and opened by the resident in the early morning hours, Manley said. All three of the packages were apparently left at the doorstep and were not delivered through the postal service or another carrier service, according to Manley.

Austin police had initially investigated House's death as suspicious, but the case has since been re-classified as a homicide, Manley said. The death of the teen Monday is also being probed as a murder, according to Manley.

Speaking before the third incident, Manley said investigators aren't sure of a motive, but can't rule out the possibility of hate crimes because the residents of both homes were African-American. He says they aren't ruling anything out, but they are no longer "making the connection to a hate crime." The victim in the latest incident is Hispanic, Manley said.

Bomb-sniffing dogs were reportedly at the scene of the explosion Monday morning and nearby homes were evacuated. Police initially were concerned about a second package at the home, but have since cleared it and believe it to be unrelated, Manley said.

The explosions happened with hundreds of thousands of visitors in the city for the South by Southwest music, film and technology festival.

The FBI is helping Austin police in the investigation. The ATF was also responding to assist. Authorities are searching nearby homes for any external video cameras that may be able to offer clues.