Dick Costolo is stepping down from his position as chief executive at Twitter. Effective July 1, Twitter co-founder and Square CEO Jack Dorsey will take over as interim CEO while the company searches for a permanent replacement.

During a conference call to discuss the matter, Costolo said he first brought up the idea of leaving at the end of last year. He added that he decided to leave now versus sticking around through the CEO search as it might cause scrutiny to intensify.

It was revealed that because Costolo stepped down voluntarily, he would not be receiving a severance package.

Dorsey will be returning to a familiar position at Twitter as he was the company's original CEO. He was replaced by fellow co-founder Evan Williams in 2008 when he transitioned to board chairman. Nearly two years later to the day, Williams elected to step down and was replaced by Costolo who served as the company's COO up to that point.

Dorsey will stay on as Square's CEO during the search, Twitter said.

The search for a new CEO will be overseen by Peter Currie, the lead independent director of Twitter's board. He'll be aided by Williams and early investor Peter Fenton and together with the help of a leading executive search firm, will conduct a global search for the next big bird.

Earlier rumors suggested Adam Bain, the company's head of revenue and partnerships, or CFO Anthony Noto might get the nod if Costolo were to exit anytime soon. No word yet on whether either will be considered during the search.

Image courtesy Lionel Cironneau, Associated Press