What may have sounded like a car backfire to some in the downtown Los Angeles area Thursday evening was actually an explosion that took place in a small building behind Bembis Meat Market around 6:30p.m. According to the LA Times, police are saying that the building was used to stored nitrous oxide cylinders for use on go carts and mini-bikes for a small business, although a lack of signage points to uncertainties of whether or not a legitimate business was actually run there. Check out the CBS news report above.

Four individuals were taken to the hospital after the explosion occurred with one unnamed victim dying at the hospital due to his injuries. Police are still investigating the cause of the explosion and are conducting a high-profile probe in the case due to the death of the single individual, according to the LA Weekly blog.

What exactly happened in the small un-marked back building Thursday night on South Grant Avenue is still uncertain as fire department arson investigators, LA Police Department detectives and investigators with the California Occupational Safety and Health Administration try to piece together the facts. Although nitrous oxide cylinders were found in the building, LA Fire Department Chief Mario Rueda declined to say if they were tied to the explosion on Thursday according to the LA Times.

The victims in the explosion have only been identified as two males and two females with little else released, although two were said to be in fair condition Thursday night. Witnesses to the scene reported seeing rescuers carry one victim out covered in blood who appeared to be missing limbs, the LA Times reports. The LA Weekly blog is also reporting that the owner of Bembis Meat Market, Ayman Eldik, told them that two females covered in blood came pounding at the back door of the meat market right after the explosion occurred.

Nitrous oxide is not an explosive but can react violently if handled improperly, such as exposed to certain elements. Cylinders used to contain the gas can also become compromised with instances such as exposure to extreme heat or flame, causing a violent release of pressure to occur if the cylinders fail. Police are looking into the possibility that an someone was filling a nitrous oxide tank for the supposed business at the time of the explosion.