Background: Sangakkara was born to Kumari Surangana and Swarnakumara Sangakkara, an attorney-at-law at Matale, Sri Lanka in 1977. His parents settled in Kandy, where he spent his childhood. Sangakkara received his primary and secondary education at Trinity College, Kandy, an independent elite private boys' school situated in the central highlands of Sri Lanka. He has two sisters: Thushari and Saranga, and an elder brother: Vemindra, all who have made national-level achievements during their schooling.
Context: In February 2009, the then captain of the Sri Lankan side, Mahela Jayawardene announced that he would step down from captaincy "in the best interests of the Sri Lankan team". He said he believed that it would give his successor around two years to build up to the 2011 Cricket World Cup. Therefore, at the age of 31 and with the experience of 80 Tests and 246 ODIs, Sangakkara succeeded Jayawardene as Sri Lanka's captain in all formats of the game. His first engagement in the role was the 2009 ICC World Twenty20 hosted by England in June. Sri Lanka became runners-up in the series after winning all the game in group and knock-out stages and being defeated by Pakistan in the final. Sangakkara made 64 not-out in the final, but was unable to take Sri Lanka for the championship. Sri Lanka failed to reach to the knock-out stage of the ICC Champions Trophy in September 2009. The next Indian tour proved to be disastrous for the team, with Sri Lanka being beaten by India in Test series 2-0 and ODI series 3-1.  Sri Lankan team under the captaincy of Sangakkara gained momentum and won the next Tri-series in Bangladesh, Zimbabwe and Sri Lanka, beating India as well. The Sri Lankans' tour of Australia proved to be very successful, in winning both the T20 and ODI series. This was Sri Lanka's first ever series victory in Australia.  A month in advance of the 2011 World Cup in March, Sangakkara decided that he would resign the captaincy after the tournament. Sri Lanka reached the final of the tournament. Throughout the tournament Sangakkara was in prolific form with the bat scoring 465 runs from 9 matches and was the third highest run-scorer behind teammate Tillakaratne Dilshan and India's Sachin Tendulkar. Days after guiding Sri Lanka to the finals of the World Cup, Sangakkara announced to the public he was stepping down as captain of the T20 and ODI teams. He offered to continue as Test captain if deemed necessary for transition to new skipper, but Dilshan was appointed captain across all formats. Reflecting on the decision afterwards, he said that "captaining Sri Lanka is a job that ages you very quickly ... It's rarely a job you will last long in ... I also had a two-year stint, and I enjoyed it at times, certainly on the field where our results showed we were one of the top two sides in the world for one-and-a-half years, especially in the shorter form of the game."  The same year, he was named the ODI Cricketer of the Year at the ICC awards ceremony. In 2012, he was honored as one of the Wisden Cricketers of the Year.
Question: How did he become captain?

Answer:
In February 2009, the then captain of the Sri Lankan side, Mahela Jayawardene announced that he would step down from captaincy "in the best interests of the Sri Lankan team".