South African police say they have uncovered a weapons cache and a large quantity of money at the Johannesburg house where four police officers and eight suspects were killed in a bloody confrontation on Sunday.

Police say the cache of weapons included a large quantity high calibre weapons, including AK-47 automatic rifles. The weapons were found in the ongoing forensic examination of the house at Jeppestown, a so-called inner city suburb in Johannesburg. In addition, police say they found tens of thousands of dollars in cash.

The shootout occurred following a robbery by a large gang of heavily armed men at a store in Honeydew, one of the city's northern suburbs. Police arrested a single suspect at the scene who led officers to the Jeppestown house.

The house was surrounded and armed police officers entered the premises. Only once they were in the house did the occupants open fire, prompting police to say that the gang seemed well trained and well organized. As a result, police say they will also investigate whether or not the suspects have had any formal military training.

Also Monday, police released three individuals arrested following the shootout, saying they were simply neighbors who are no longer under suspicion. Eleven suspects remain in detention and are expected to appear in court Tuesday.

The incident is the latest in a series of violent incidents that have shocked South Africans who are used to high, if declining, levels of violent crime. In recent weeks, several motorists on the roads in and around Johannesburg have been murdered without vehicles or other property being stolen from the victim. While police say at least one may have been a botched car-jacking, the others appear to be random.

Boyane Tshehla who heads the Crime and Justice Program at the Institute for Security Studies in Pretoria says that in the latest incident, the number of criminals and their apparent level of expertise, is of great concern. "It is one of those shocking incidents. In no way I think isolated in terms of, it is happening. But I think in magnitude it is something that is quite worrisome. If you look at the number of people involved there, it is quite a concern. I think what it says to anyone looking at it, should be that we are dealing with quite organized people, we are dealing with well equipped people, and from the look of it, quite technical people," he said.

Safety and Security Minister Charles Nqakula said Monday that while it is always preferable that suspects are arrested and prosecuted, police have a right when threatened by weapons to protect themselves.