LAHORE Police and intelligence agencies have jointly begun investigations in connection with Mondays suicide attack on Special Investigation Agency (SIA) building in Model Town and picked up several suspects as the death toll climbed to 15 on Tuesday. Sources close to the investigators revealed that on the basis of information obtained from the arrested militants, more raids were being carried out in various parts of the province to capture those involved in the barbaric act. The sources said Crime Investigation Agency (CIA) police arrested four terrorists from various parts of the provincial metropolis during successful operation carried out in the wee hours of Tuesday. As a massive crackdown has been launched against the suspects, the law-enforcement agencies are on a red alert with heavy deployment around the key official installations to avoid further untoward happening. The arrested suspects, said to be the members of Tehrik-e-Taliban Afghanistan, are identified as Muhammad Yasin alias Junaid/Jamshed, Muhammad Kamran alias Zarar, Abubakr alias Suleman and Khurshid Ali. The arrested men have been shifted to some unknown location where a joint team, comprising senior police officers and intelligence personnel, is interrogating them. According to police sources, the total number of arrested persons is 20. Security has also been put on high alert on the entry and exit points of the City to keep a vigilant eye on the activities of the miscreants. The investigators have also sent the particulars and other materials collected from the blast site to the chief chemical examiner for laboratory tests. The parts of a Toyota Hiace single cabin, used in the blast, have been sent to laboratory for further investigations, Capital City Police Officer (CCPO) Rathore said. On the other hand, the policemen and civilians, martyred during the Mondays attack, were laid to rest at different graveyards. Hundreds of local residents, political leaders and senior officials attended their funeral prayers. Earlier, the doctors at Emergency Ward in Jinnah Hospital said 17 victims of blast were still under treatment in the hospital but their condition was stable now. Only one patient is still in the Intensive Care Unit (ICU), whose condition is serious, one doctor said. Talking to The Nation, Principal Allama Iqbal Medical College Prof Dr Javed Akram said out of a 71 injured, 50 victims were discharged from Jinnah and General hospitals, while remaining were being provided free medical treatment under the supervision of a team of specialised doctors. The condition of the victims at General Hospital, Ittefaq Hospital, Sara Memorial Hospital and Sheikh Zayyed Hospital is also stated to be stable till filing of this report. A rescuer said a head was recovered from the debris of SIA demolished building on Tuesday. Police, however, claimed that the head was identified of a constable martyred during the blast, who was discharging his duty when the terrorists struck the building. The martyred including Mohammad Naveed (18), Raheela (5), Ghazala Hussain (47), Habib Ahmad (40), Gulzar (27), Arif Sadiq (45), Munawar Alam (30), SIA Inspector Mohammad Aslam (40), Ahmad Bilal, Abdul Aziz (40) and Mohammad Afzal (35) were identified soon after the blast. Edhi sources, however, claim that almost 21 people were killed in the terror strike, adding that 13 of them had been identified while the identity of seven others was confirmed yet.