FORT WORTH -- No work by Mozart has generated quite as much controversy as his Requiem. That it is a work of genius few would deny. The question is: How much of it is actually by Mozart, and how much is the work of one or more other composers?The question arises because Mozart died while composing the Requiem. He left only one completed movement (the opening one). There is a lot of other material in his hand, but much of it is in the form of sketches or drafts. After his death, his widow asked one of his friends and close associates, Franz Xaver Süssmayr, to complete the work. Süssmayr complied.That is the standard story, but virtually a whole industry has arisen questioning the details and proposing alternate theories.Some say that other composers of Mozart's time were involved in Süssmayr's completion. Others question Süssmayr's claim that the desperately ill Mozart gave him instructions about completion and even some written material (none of which has turned up).In modern times at least seven scholars, dissatisfied with Süssmayr's work, have come up with completions of their own. None has won acceptance by the musical public.Even fictional works have taken up the controversy. Pushkin wrote a play about the creation of the Requiem, which Rimsky-Korsakov turned into an opera. The Requiem plays a substantial role in Peter Shaffer's play (and movie) Amadeus.The Fort Worth Symphony Orchestra, four soloists and the Texas Christian University Chorale offered an opportunity this week to reconsider Mozart's and Süssmayr's work. The performance was Thursday night in the Arborlawn United Methodist Church.Probably part of the animus toward Süssmayr comes from the audacity of a minor composer in taking up the task of completing a major work by one of the supreme geniuses of music.Yet there's a reason Süssmayr's version has persisted. He did his job well, so well that it's hard to hear any drastic drop in quality from what is unquestionably Mozart's work to what is undeniably Süssmayr's.The most striking point is the Lacrymosa movement. We know that Mozart wrote the first eight measures and left the rest unfinished. Yet it is achingly beautiful through to the end. Either Süssmayr was a much more accomplished composer than he is usually given credit for, or those written notes from Mozart that he claimed he had really did exist.At any rate, Thursday's performance was a consistently emotional tribute. The chorale was a unified and subtle performing group, the solo quartet was of high quality, and Miguel Harth-Bedoya captained a moving interpretation. The soloists were soprano Hannah Rigg, mezzo Marisan Corsino, tenor Derek Chester and bass-baritone Derrada Rubell-Asbell.The church was quite resonant (more so than the Bass Hall), a fitting detail since the Requiem was written for church performance, of course. Beautiful stained glass illuminated by the setting sun was a visual enhancement.