New Delhi: Investigations into the vandalism of DTC and cluster buses during protests over the past few days have revealed that several third-party contractual workers engaged by the transport corporation as drivers were allegedly involved in damaging the buses, with police so far having apprehended 17 people in connection with the incidents.Police sources said eight people were apprehended in Kanjhawala and four others at different locations in Rohini district in connection with two FIRs. Investigators have also found a WhatsApp group allegedly being used to discuss plans to vandalise DTC buses. Three people were allegedly running the group, where members discussed the targeting of buses, plans of the attacks and other details, police said.In Dwarka, 17 cases have been registered in connection with incidents of vandalism, while five people have been arrested so far. More than 50 people have also been detained under Section 65 of Delhi Police Act for questioning in connection with the incidents.In the Dwarka case, police received a PCR call at 5:52 am on Sept 19 after windows of four cluster buses were broken in Pochanpur. A case was registered. Police examined CCTV footage and found a person wearing a DTC uniform allegedly throwing stones at the buses. He was identified as Manoj Sharma (31), a driver of one of the buses involved in the incident.In a separate case at Baba Haridas Nagar, PCR calls were received on Sept 18 regarding damage to the windows of DTC buses. Two FIRs were registered on Sept 19 under Section 3 of Prevention of Damage to Public Property Act on the complaints of some bus drivers.Police examined CCTV footage and based on identification by the complainants nabbed three contractual DTC drivers: Sandeep (42), Ram Singh (50) and Munni Lal (42).Investigators alleged that they were on a motorcycle and, whenever they got an opportunity, damaged the windows of DTC buses by throwing stones or using a slingshot. A motorcycle and a slingshot were seized from them, police said.