yo 'smabhyaḿ sampratiśrutya
kanyā-ratnaḿ vigarhya naḥ
kṛṣṇāyādān na satrājit
kasmād bhrātaram anviyāt
yah -- who; asmabhyam -- to each of us; sampratisrutya -- promising; kanya -- his daughter; ratnam -- jewellike; vigarhya -- contemptuously neglecting; nah -- us; krishnaya -- to Krishna; adat -- gave; na -- not; satrajit -- Satrajit; kasmat -- why; bhrataram -- his brother; anviyat -- should follow (in death).
Since Satrajit's brother, Prasena, had been violently killed, the implication of "following his brother's path" is obvious. What we have here is an assassination plot.
It is well known that both Akrura and Kritavarma are exalted, pure devotees of the Supreme Lord, so their unusual behavior requires some explanation. The acaryas provide it as follows: Srila Jiva Gosvami states that Akrura, although a first-class, pure devotee of the Lord, was a victim of the anger directed against him by the residents of Gokula because he took Lord Krishna away from Vrindavana. The gosvami further states that Kritavarma had associated with Kamsa -- both of them being members of the Bhoja dynasty -- and thus Kritavarma was now suffering from this undesirable association.
Srila Visvanatha Cakravarti offers an alternative explanation: Both Akrura and Kritavarma were furious with Satrajit because he had insulted Lord Krishna and spread false rumors about Him in Dvaraka. Under normal circumstances Akrura and Kritavarma would have been most pleased that Lord Krishna married the beautiful Satyabhama. Being pure devotees, they could not actually be unhappy about this match, nor could they become jealous rivals of the Lord. Therefore they had an ulterior motive in behaving like His rivals.