Nawab Momin khan remained the deputy governor (under various governors) of Lahore district in Punjab under Mughal government for about 28 years. In 1726 A.D. Zakriya Khan was appointed the governor of Lahore and he kept Momin Khan as his deputy governor. Only under Zakriya Khan did Momin Khan gained his popularity as "murderer of Sikhs". He was against all non-muslims but with Sikhs he broken all norms of civility. He would just capture any Sikh and order to be killed., he told all the Hindus around Lahore to shave off their beards. He was also responsible for the murder of Bhai Tara Singh of village 'Wan', as well as Shaheed Bhai Taru Singh .
Zakriya Khan died on 1st July 1745 and then his son Yahya Khan became the governor of Lahore keeping Momin khan as his deputy governor. In 1747 when Yahya khan's brother Shah Nawaz Khan imprisoned Yahya and became governor of Lahore he kept Momin Khan as his deputy governor. Then from april 1748 till november 1753 he was deputy governor under Meer Mannu. Momin khan used to round up Sikh women and children and murdering them at Lahore's horses market, which was later renamed as Shahidganj when Lahore came under Sikh rule.
In 1754, Momin Khan did became governor of Lahore for few days reverting back to his post of Deputy governor under new governor as appointed by Mughals. At his old age Momin khan starting inflicting more cruelties, he would often capture the relatives of Sikhs murdering them. Thus, Jathedar Kapur Singh decided to do something about Momin Khan. He at a sikh congregation asked if any Sikh is brave enough to bring him the cloved head of Momin Khan. This was not an easy job, Momin Khan was a high ranking Mughal officer with over 100 personal attendants all the time. Sardar Aghar Singh accepted the challenge and asked for an Ardas. Sardar Aghar Singh was nephew of Bhai Mani Singh ji Shaheed. Aghar Singh asked congregation for permission to go into the city of Lahore in disguise then murdering and cloving the head of Momin khan. The sikh congregation responded it with the war cries of "Jo Bole So Nihal, Sat Sri Akal" and thus after Ardaas and getting the permission from sarbatt Khalsa Sardar Aghar Singh was sent to Lahore in almost exact similar fashion as earlier Bhai Mahtab Singh of Mirankot and Bhai Sukha Singh Mari Kambokiwala were sent to Amritsar to murder Massa Ranghar. Aghar Singh reached Lahore pondering over various schemes to fulfill this task. He opened up his turban and threw his hair over his shoulders, giving a twist to his turban from the end making it look like a Muslim from the other end of river Ravi.
At Lahore, Sardar Aghar Singh started friendship with servants of Momin Khan. Nobody could recognize him in this disguise as a Pachada Muslim of Ravi. Even Momin Khan started trusting him. Soon Nawab Momin Khan made him his personal attendant. One day Momin Khan went to stroll by the river Ravi alone with Sardar Aghar Singh. Seeing the oppurtunity Sardar Aghar singh cloved Momin Khan's head with one strike and galloped back to the camp of Jathedar Kapur Singh. Jathedar Kapur Singh presented Sardar Aghar Singh with a special sword and the Sikh congergation thanked God for having gotten justice of murders of Innocent Sikh.