The quantum of punishment will be announced tomorrow.
Special Court Judge Gyaneshwar Prasad Srivastava held Shahabuddin guilty of involvement in the attack on Singhal in Siwan district on May 3, 1996.
Besides Shahabuddin, his police guards Jehangir and Khali, at the time when he was the RJD MLA from Ziradei district, were also convicted.
The trio was convicted under sections 307 (attempt to murder) and 353 (assault or criminal force to deter public servant from discharge of his duty) of the Indian Penal Code, besides section 27 of Arms Act.
Singhal had gone to Darauli-Mathiya village after receiving information that there was tension. While returning to Siwan, he saw armed people at Done Bazaar and sent his bodyguards to inquire. Seeing policemen approaching them, the men tried to flee with the SP chasing them.
Shahabuddin and his men then began firing on SP's vehicle, who escaped unhurt.
It is for the fourth time that Shahabuddin has been convicted in the last six months.
Earlier on March two Shahabuddin, a key Muslim leader of RJD, was sentenced to two years rigorous imprisonment in a case of attack on CPI-ML office at Kurmabad in Siwan town on September 19, 1998, in which party office secretary Keshav Baitha was kidnapped and assaulted by the MP and his henchmen.
On May 8, the incarcerated MP was sentenced to life imprisonment by a special court of additional district and sessions judge Gyaneshwar Prasad Srivastava in connection with the kidnapping and suspected murder of CPI-ML worker Chotelal Gupta on February 7, 1999.
The prosecution was unable to establish the charge of murder as Gupta's body was not found.
Shahabuddin was recently sentenced to three years rigorous imprisonment in a case of stolen vehicles.
The RJD MP is facing about 30 cases ranging from murder and attempt to murder to possession of illegal firearms of foreign make, besides under the Foreign Exchange Maintenance Act and Wildlife Act.
Among cases pending against him are that of murder of former Jawaharlal Nehru University student union president Chandrashekhar on March 31, 1997.
He is also an accused in the case of an encounter with police at his Pratappur village on March 16, 2001, in which a policeman was killed after a cache of firearms, including AK 47 assault rifles, and explosives were seized though Shahabuddin himself managed to escape.