A police crime scene van arrives near the site of Sunday's deadly explosion, Monday, March 19, 2018, in Austin, Texas. Police warned nearby residents to remain indoors overnight as investigators looked for possible links to other package bombings elsewhere in the city this month. (AP Photo/Eric Gay)

AUSTIN, Texas – Austin police officers have completed a sweep of the neighborhood where the latest in a string of bombings occurred and deemed it safe, but they are asking residents to remain indoors for several more hours.

Police Chief Brian Manley said at a news conference today that although officers didn’t find anything suspicious while canvassing the southwestern Austin residential neighborhood of Travis Country, investigators are still collecting evidence.

The four bombings that have killed two people and injured four others in Texas’ capital city this month are believed to be the work of a serial bomber.

Authorities say Sunday night’s bombing differed from three earlier this month. Two men received significant injuries in Sunday’s attack. It apparently involved a bomb placed alongside a fence and a tripwire that the men triggered while walking their bikes between the fence and a street.

The first three attacks used package bombs left on people’s doorsteps. Those attacks killed two people and injured two others.

Authorities are urging the public to provide surveillance video that could assist in the investigation into the string of bombings in the Texas capital of Austin.

The police chief asked homeowners and others to forward video to investigators that might offer insight into the bombing Sunday night or three earlier this month.

The latest explosion injured two men in their 20s who were riding or walking their bicycles through a neighborhood in southwestern Austin. The earlier blasts killed two people and injured two others and happened in other parts of the city.

Authorities say the device that detonated Sunday featured a tripwire and was left near a road, while the prior bombings involved packages left on people’s doorsteps.