Mexico City, Mexico (CNN) -- Mexican authorities have bolstered their search for a missing U.S. citizen and the government rejects assertions that security forces aren't doing enough to find him, the foreign ministry said Friday. David Michael Hartley has been missing since a reported pirate attack September 30 on a lake bisected by the U.S.-Mexico border. Hartley's wife, Tiffany, told authorities her husband was shot and killed by pirates on Falcon Lake during a sightseeing trip. His body has yet to be found, leading to questions about the accuracy of her statements. The ministry said the federal attorney general's office opened an investigation based on testimony Tiffany Hartley gave to Mexican authorities at the consulate in McAllen, Texas. The government also has been in close touch with several U.S. authorities.
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NEW: Mexico says it has ramped up the search
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Wife, her story questioned, tells HLN, "I know what I know"
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Sheriff calls on drug cartels to turn over the body
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Tiffany Hartley said men in motorboats shot her husband
Despite the dangers on the Mexican side of the lake, Texas officials on Thursday said that the @placeholder side of the body of water remains safe.