This was confirmed by Home Minister Ramesh Chennithala shortly after the state Cabinet decided to seek a CBI probe, after which the slain leader's wife called off her five-day indefinite fast.
While sections in CPI(M) expressed doubts about the veracity of the letter, a personal aide at Achuthanandan's office confirmed that such a letter had been sent.
While addressing a press meet, Chennithala read out contents of the letter in which Achuthanandan said he expected the government would consider Rema's demand.
The nonagenarian leader also said government's attitude towards Rema's struggle had been negative and no action was taken on a petition submitted by her a month back.
Slain leader's wife called off her five-day indefinite fast.
He pointed out that the government had not taken any step on the matter despite the advice of Director General of Prosecution that a further a probe was possible.
Cashing in on the divide in CPI(M) over the issue, Chennithala said Achuthanandan's letter could be treated as the view of the entire LDF on the issue since he is the leader of Opposition in the Assembly.
The procedures for recommending a CBI probe would be completed soon since even the Opposition had supported such a course of action, Chennithala added.
Earlier also, the disconnect between Achuthanandan and the CPI(M) state unit controlled by its secretary Pinarayi Vijayan on the issue had come to the fore.
A couple of weeks ago, the party had expressed open resentment against Achuthanandan for making some remarks supporting the RMP's demand.
The Marxist stalwart also embarrassed the party by visiting Chandrasekharan's family members to share their sorrow and distancing himself from the state's leadership stand that the slain leader from Onchiyam was a "renegade."