"We have questioned four MK officials," National Police deputy chief intelligence Inspector General Mathius Salempang said here on Tuesday.
Due to the forgery Dewi Yasin Limpo from the People`s Conscience Party (Hanura) failed to sit in the House of Representatives (DPR).
Salempang said the MK officials being questioned were those who knew exactly about the process of the MK letter and the evidence was also available.
He did not tell the number of evidence collected from the MK officials.
The police have so far questioned 19 witnesses linked to the case.
The police earlier said they had discovered the copy of the 2009 MK letter on the failure of Dewi Yasin Limpo to sit in the DPR to represent South Sulawesi.
When Dewi Yasin Limpo`s election as a DPR member was canceled by the General Elections Commission (KPU) because MK ruled that KPU had used a forged ruling she got angry and reported MK to the police.
Dewi accused MK of having abused its authority by stating that the winner was Misriani from the Gerindra Party.
MK chief Mahfud MD later reported Andi Nurpati then a KPU official for allegedly having forged the MK ruling document.
It is believed some words in the document have been replaced.