Law enforcement authorities in Austin, Texas, warned residents not to open suspicious or unexpected packages.

If a package arrives unexpectedly or appears suspicious, authorities warn to leave it outside and call 911 for assistance.

“If you receive a package that you are not expecting or looks suspicious, DO NOT open it, call 911 immediately,” Austin Police Chief Brian Manley tweeted.

If you receive a package that you are not expecting or looks suspicious, DO NOT open it, call 911 immediately. RT- Help us spread this message. https://t.co/j9bxbaaBce — Chief Brian Manley (@chief_manley) March 12, 2018

Three packages exploded during the past 10 days in the Austin area–including two on Monday.

It appears the packages were not sent through the mail or another delivery service but were left on the doorsteps of the homes, the Austin American-Statesman reported. Austin interim Police Chief Brian Manley warned the community not to take any package that is left outside their home inside.

Authorities are not releasing any details about the devices but said they know what type of explosives were used.

The FBI and ATF are assisting the Austin Police Department in the investigation of the three cases. The matter is being investigated as a homicide. Manley said Monday’s first explosion is similar to the March 2nd explosion and is “likely related.”