Crews have found the body of a fourth person who died in an explosion at a San Antonio construction company and investigators worked Monday to determine the cause and origin of the blast.

The blast happened late Friday at K-Bar Services and could be heard miles away, the San Antonio Express-News reported. Responders immediately found one person dead when they arrived, then two more bodies were discovered on Saturday.

The San Antonio Fire Department said a fourth victim was discovered Sunday.

TEXAS SEES OVER 2,500 MIGRANTS CROSS THE BORDER IN MERE 24-HOUR SPAN

"This is an extremely active case," SAFD spokesman Joe Arrington said Sunday. "The fire department’s Arson Bureau has taken the lead on this case and are working with SAPD, the FBI and ATF to confirm what happened that night."