Charges have been dropped for two people accused of conspiracy to murder.

Two teenagers and an older man faced court on Monday, but two of the men, a 20-year-old Kilburn man and a 15-year-old boy from Park Holme were released from custody without charge.

The trio were arrested over the weekend and electronic equipment was seized.

The 17-year-old from Huntfield Heights has also had his conspire to murder charge withdrawn, however he attended the Adelaide Youth Court on other charges including possessing an object with intent to kill or endanger life, possessing a prohibited weapon and assault.

A fourth boy, a 17-year-old from Morphett Vale was reported on Sunday afternoon with supplying a prohibited weapon and will face Christies Beach Youth Court at a later date

South Australian police said the investigation would continue as they review a large amount of electronic evidence.

"Police have not ruled out charges being laid again at a future date," SA Police said in a statement on Monday night.