Johannesburg - Several senior police officers investigating Czech fugitive Radovan Krejcir and some of his alleged victims are believed to have been the targets of murder plots.

Encrypted iPhones and iPads taken by the police from four alleged hitmen last week are said to contain detailed information about at least 10 police officers in a specialised team investigating Krejcir. These officers were all allegedly to be killed.

The information retrieved from equipment taken from Siboniso Miya, 32, Jacob Nare, 28, Owen Serero, 32, and his girlfriend, Zodumiso Biyele, 23, is believed to be crucial in attempts to uncover the identity of the mastermind of a foiled assassination plan.

The four appeared in the Alexandra Magistrate's Court, northern Johannesburg, yesterday on several charges relating to allegations of a failed assassination attempt on police crime intelligence officer Colonel Nkosana "Killer" Ximba and on private forensic investigator Paul O'Sullivan on Thursday.

The four are to face charges of conspiracy to commit murder, robbery with aggravating circumstances, vehicle theft, and the illegal possession of firearms and ammunition. They were arrested in a dramatic raid on the Rivonia Road Lodge, Johannesburg.

A crime intelligence source said the police had learned that the planning of the alleged assassinations began last month.

"The [surveillance] programs on the phones and computers that were confiscated are highly sophisticated ... not available to just anyone. They allow you to trace people to within a few metres of their location," O'Sullivan said.

Information that O'Sullivan had in his possession indicated that the four had once worked for Krejcir.

"There is information that shows they have been in telephone contact with Krejcir while he was in prison over the past few weeks.

"The phones and computer devices were programmed with sophisticated software [usually] available only to law-enforcement agencies.

"With this software, when you input a cellphone number, you see exactly where the person is."

Police spokesman Lieutenant-General Solomon Makgale said the four were allegedly targeting "all the members of the investigating team."

Makgale would not say how many officers were on the team.

Krejcir and his co-accused were arrested in November for the alleged kidnapping, assault and attempted murder of the brother of a Krejcir business associate.

The man was alleged to have been kidnapped and tortured because the associate was believed to have stolen 25kg of the drug known as tik from Krejcir, which he was to have smuggled into Australia in June.

Miya is to appear in the Palm Ridge Magistrate's Court later this month alongside Krejcir and his co-accused, Desai Luphondo, and Hawks warrant officers Samuel Maropeng and Jeff Nthoroane.

Miya was arrested on Thursday at a Sandton restaurant hours before the police caught Biyele and Serero at the Rivonia Road Lodge.

Nare was arrested on Saturday .

Makgale said a policeman who worked with Maropeng and Nthoroane was on the run.

He said investigations had revealed that Serero had nine outstanding warrants of arrest for hijacking against him.

National Prosecuting Authority spokesman Nathi Mncube, who refused to comment on the charges, said that because of the assassination allegations a risk assessment was being made ahead of the accused's bail application.

"We will ensure there is necessary protection for all our staff."

The four were remanded and will appear in court again on Monday.

Miya's lawyer, Cronje Kriel, said he was unaware of his client's court appearance with Krejcir.

"I will consult him today. Other than seeing my client in court, I have not spoken to him. I don't even know where he is being held."