Twiiter CEO Dick Costolo will step down. Chairman Jack Dorsey, the social network’s co-founder and former chief executive, will serve as interim CEO, starting July 1. Costolo will remain on the board. “There is no one better than Jack Dorsey to lead Twitter during this transition,” Costolo said in a statement. “He has a profound understanding of the product and Twitter’s mission in the world as well as a great relationship with Twitter’s leadership team.” Dorsey said he will remain CEO of Square, the mobile payments service he co-founded in 2009. Costolo denied that he was forced out of his position. He said he approached the board about stepping down late last year; and as criticism of his leadership ramped up in recent months, he felt that remaining in office would harm the company’s attempts to find a replacement. “I personally felt that the scrutiny of the company would intensify if I remained CEO during the search process,” he said.