Guardian: BP shares jumped this morning after a US investigator pointed the finger at Halliburton which, as a contractor to BP, was responsible for cementing the blown-out well in the Gulf of Mexico. However, he also noted that BP was aware of flaws in the cement used to seal the Deepwater Horizon well. BP was one of the biggest gainers on the FTSE 100 in early trading, rising 5p to 428p, a gain of 1.18%. In a letter, the lead investigator for the presidential commission on the oil spill, Fred Bartlit,…